[media] si2157: cancel_delayed_work_sync before device removal / kfree

si2157_remove  was  calling  kfree(dev)  with  possibly  still  active
schedule_delayed_work(dev->stat_work).  This  caused kernel  panics in
call_timer_fn e.g. after rmmod cx23885.

Signed-off-by: Ernst Martin Witte <emw-linux-kernel@nocabal.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/tuners/si2157.c

@@ -458,6 +458,9 @@ static int si2157_remove(struct i2c_client *client)
 
 	dev_dbg(&client->dev, "\n");
 
+	/* stop statistics polling */
+	cancel_delayed_work_sync(&dev->stat_work);
+
 	memset(&fe->ops.tuner_ops, 0, sizeof(struct dvb_tuner_ops));
 	fe->tuner_priv = NULL;
 	kfree(dev);